BOULDER, Colo. Scientists have detected a major solar flare erupting on the sun that could buffet Earth with a geomagnetic storm in the next two days.

The blast of charged solar particles already is producing scattered radio blackouts but is not expected to significantly disrupt telecommunications or electrical power. It might generate a dramatic light show for midnight stargazers in the northern latitudes until early Saturday.

The sun is approaching the height of its 11-year storm cycle. Unlike previous cycles, this period has been relatively quiet, with eruptions every two months or so.

This storm is estimated to be 20 times stronger than a solar flare in early April.

"Finally, the sun is beginning to flex its muscles," said solar forecaster Dave Speich of the federal Space Environment Center in Boulder.

The latest eruption came at midday Tuesday from a cluster of sunspots on the upper left of the sun as viewed from Earth. A powerful X-ray flare ejected an estimated billion tons of charged particles into space.

Riding the solar wind at speeds up to 2 million mph, the particles should zap Earth's magnetic field late Thursday or early Friday. The sunspot cluster could be active another eight days.

Solar flares can create electrical disturbances that disrupt power supplies, telecommunications and signals that control pipelines and other systems. The particles can damage satellites and alter their orbits.

The storm is rated as moderate on the federal government's new space weather scale.

In 1989, a severe solar storm knocked out power stations serving Canada and the northeastern states, as well as an electrical transformer in New Jersey. Since then, power grid and satellite operators have taken steps to protect their systems.

The clouds of charged particles also produce the aurora borealis, or northern lights. Weather permitting, the light show from this storm could be visible as far south as Washington, D.C.